Field of the Invention
The present invention relates to an image process of reconstructing a translucent body in consideration of internally-scattered light.
Description of the Related Art
In recent years, in the computer graphics (CG) field, a technique of rendering a translucent body not only on the surface of which but also in which light is scattered has been developed. Especially for the human skin, not only reconstruction of internally-scattered light but also reconstruction of wrinkles, pores, and the like on the surface is important, and thus the degree of difficulty of a rendering process is high. The surface shape of wrinkles, pores, and the like will be referred to as “the fine irregularity of a body surface (FIOS)” hereinafter. The translucent body is a body in which light is transmitted and scattered, such as a cloudy glass or plastic, a cloudy liquid, or a living cell.
As a method of reconstructing internally-scattered light, there is known a method disclosed in Japanese Patent Laid-Open No. 2006-506742. According to Japanese Patent Laid-Open No. 2006-506742, sampling is performed at a plurality of points, and pixel values are integrated using a Bidirectional Scattering Surface Reflectance Distribution Function (BSSRDF), thereby performing a blurring process. There is also known a method of reconstructing internally-scattered light by performing a blurring process of a different blurring amount for each of the wavelength channels of the image values. As an FIOS reconstruction method, there is provided a process using a bump map representing a surface shape. If the human skin is reconstructed by CG, a blurring process is generally executed after an FIOS is reconstructed.
The appearance of a translucent body having an FIOS influenced by internally-scattered light will be described with reference to FIGS. 1A and 1B. FIGS. 1A and 1B each show the spread of internally-scattered light in the cross section direction when light enters a translucent body 101. As shown in FIG. 1A, if light enters the surface of the translucent body 101 in the vertical direction, exit light has a feature in which long-wavelength light R spreads more largely than short-wavelength light B.
On the other hand, FIG. 1B shows a case in which light obliquely enters the translucent body 101. Light which obliquely enters has a feature of spreading in the incident direction. Thus, the right portion (to be referred to as a cut portion hereinafter) of the translucent body 101 which has been obliquely cut is originally a portion where no light enters to generate a shadow. However, since internally-scattered light exits, the cut portion becomes bright. At this time, more long-wavelength light which more readily spreads exits from the cut portion, and the cut portion which serves as the shadow portion when there is no internally-scattered light is observed to be red and bright due to internally-scattered light. The cut portion which serves as the shadow portion when there is no internally-scattered light corresponds to an FIOS such as wrinkles and pores in the case of the human skin.
The technique described in Japanese Patent Laid-Open No. 2006-506742 cannot reconstruct the feature in which the FIOS becomes red and bright, since a blurring process is uniformly performed without considering the influence of the FIOS. Since the FIOS largely influences the appearance of the translucent body, it is necessary to faithfully reconstruct the feature (to be referred to as the brightness increase hereinafter) in which the FIOS becomes red and bright due to internally-scattered light.